In the formation of color photographic paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult, requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. One defect in prior formation techniques is caused when an air bubble is trapped between the forming roller and the polyethylene layer which will form the surface for casting of photosensitive materials. This air bubble will form a pit that will cause a defect in the photographic performance of photographic materials formed on the polyethylene. It would be desirable if a more reliable and improved surface could be formed at less expense.
In color papers there is a need for providing color papers with improved resistance to curl. Present color papers will curl during development and storage. Such curl is thought to be caused by the different properties of the layers of the color paper, as it is subjected to the developing and drying processes. Humidity changes during storage of color photographs lead to curling. There are particular problems with color papers when they are subjected to extended high humidity storage such as at greater than 50% relative humidity. Extremely low humidity of less than 20% relative humidity also will cause photographic papers to curl.
In photographic papers the polyethylene layer also serves as a carrier layer for titanium dioxide and other whitener materials, as well as tint materials. It would be desirable if the colorant materials rather than being dispersed throughout the polyethylene layer could be concentrated nearer the surface of the layer where they would be more effective photographically. In U.S. application Ser. No. 08/862,708 (Bourdelais et al.) filed May 23, 1997, a composite, photographic material with laminated biaxially oriented polyolefin sheets has been proposed. While this invention does provide a solution to the sensitivity of photographic paper to humidity, it uses standard photographic base paper whose roughness is replicated on the surface of the imaging element. Traditional cellulose paper base has a particularly objectionable roughness in the spatial frequency range of 0.30 to 6.35 mm. In this spatial frequency range, a surface roughness average greater than 0.50 .mu.m can be objectionable to consumers. Visual roughness greater than 0.50 .mu.m is usually referred to as orange peel. It would be desirable if orange peel roughness could be minimized in the laminated photographic base paper.
It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene laminated to cellulose grade paper for use as a reflective receiver for thermal dye transfer imaging process. The preferred bonding agent in U.S. Pat. No. 5,244,861, to bond the biaxially oriented polypropylene sheets to paper, is low density polyethylene melt extruded from a slit die. Because of the high processing temperatures required for LDPE, shrinkage of the biaxially oriented sheet is common in the melt extrusion process. Shrinkage can cause undesirable changes in the Poisson ratio of the laminated receiver, as well as a reduction in the optical performance of the receiver. It would be desirable to reduce the extrusion temperature of the bonding layer and maintain acceptable integrity of the laminated support.
During the manufacturing process for photographic papers while the laminated photographic support is being emulsion coated and slit, the laminated structure is subjected to various forces in manufacturing that will cause delamination of the polypropylene sheet from the paper. The delamination may be a result of bonding layer failure to either the base paper or the polypropylene sheet. Also, when the photographic paper is being processed and finished at photofinishers, the laminated structure is also subjected to various forces in both the wet and dry state. Furthermore, when the photographic paper is kept for years by the final customer, the laminated structure is subjected to forces created by temperature and humidity changes that could cause delamination of the biaxially oriented polyolefin sheets from the cellulose paper base. Delamination of the biaxially oriented sheet from the paper during manufacturing will result in the product being wasted, thus increasing the cost of manufacture. Delamination of the biaxially oriented sheet from the paper at either the photofinishing operation or in the final customer format will result in a loss in the appearance of the image and the reduction of the commercial value of the photograph. It would be desirable if a melt extruded bonding adhesive could prevent delamination of biaxially oriented sheets from the base paper during manufacture of a laminated imaging support and in the final customer format.
Prior art photographic support materials typically utilize melt extruded polyethylene to waterproof the paper during the wet processing of images during the image development process. The gelatin based light sensitive silver halide emulsion generally adheres well to the polyethylene layer during manufacturing and wet processing of images. It would be desirable if a biaxially oriented sheet contained an integral bonding layer to provide emulsion adhesion during emulsion coating and the wet processing of images during the image development step.
Commercially available photographic paper typically has a single color logo identifying the manufacturer of the photographic paper. This logo is applied to the backside of the photographic paper and is generally printed on the base paper before the polyethylene coating is applied. The present product is practically limited to a single color because the present production machines are limited by cost and space limitations to a single color press for the printing of indicia onto the back of the base paper. It would be desirable if a low cost method of applying multiple colors to the backside of photographic paper were available.
Present photographic papers are typically designed to have a life of one hundred years or greater to preserve images across several generations. Present photographic papers generally being constructed of polyethylene coated cellulose paper can be easily damaged, torn, or abraded as images are viewed and handled by consumers over one hundred years. It would be desirable if a photographic paper support was more durable, offering the consumer a photographic image that would better withstand one hundred years of handling and viewing.